1. Field of the Invention
The present invention relates to coatings for medical devices such as stents.
2. Description of the State of the Art
Stents act as scaffolding structures, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location. Mechanical intervention via stents has reduced the rate of restenosis as compared to balloon angioplasty; restenosis, however, is still a significant clinical problem. Treating restenosis in stented vessels can be challenging, as clinical options are more limited as compared to lesions that were treated solely with a balloon.
In order to more effectively treat restenosis, stent implantation procedures are being supplemented with a pharmaceutical regimen. Systemic administration of drugs for the treatment of restenosis can produce adverse of toxic side effects for the patient. Local delivery is a preferred method of treatment in that smaller to total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery thus produces fewer side effects and achieves more favorable results.
Being made of metal, stents need to be modified so as to provide a suitable means of locally delivering a drug. A polymeric coated stent has proved to be a very effective way of allowing a stent to systemically deliver a drug. A solution of a polymer dissolved in a solvent and a therapeutic substance added thereto is applied to the stent and the solvent is allowed to evaporate. Accordingly, a polymeric coating impregnated with a therapeutic substance remains on the surface of the stent.
To the extent that the mechanical functionality of stents has been optimized, continued improvements can be made to the coating of the stent. For example, the biocompatibility of the polymeric coating can be improved. The embodiments of the present invention provide different methods of enhancing the biocompatibility of polymeric coatings.